U.S. patent application number 11/272024 was filed with the patent office on 2006-06-08 for resin-coated ferrite carrier for electrophotographic developer, its production method, and electrophotographic developer using the resin-coated ferrite carrier.
This patent application is currently assigned to POWDERTECH CO., LTD.. Invention is credited to Toshio Honjo, Kanao Kayamoto, Tetsuya Uemura.
Application Number | 20060121385 11/272024 |
Document ID | / |
Family ID | 35705248 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060121385 |
Kind Code |
A1 |
Uemura; Tetsuya ; et
al. |
June 8, 2006 |
Resin-coated ferrite carrier for electrophotographic developer, its
production method, and electrophotographic developer using the
resin-coated ferrite carrier
Abstract
A resin-coated ferrite carrier having a uniform resin coating
and emitting no offensive odors, etc., its production method, and
an electrophotographic developer which comprises the resin-coated
ferrite carrier, is excellent in the charge stability and image
quality stability over a long period, causes less fogging of image
or carrier adhesion, is favorable in the image density and
environmental dependency, and can fully respond to high-speed and
full-color imaging, are provided. The resin-coated ferrite carrier
for the electrophotographic developer is characterized in that the
surface of ferrite particles is coated with a mixed resin of a
tetrafluoroethylene-hexafluoropropylene copolymer or a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer and a
polyamideimide resin, and that the mixed resin contains a silicon
oxide.
Inventors: |
Uemura; Tetsuya;
(Kashiwa-shi, JP) ; Honjo; Toshio; (Kashiwa-shi,
JP) ; Kayamoto; Kanao; (Kashiwa-shi, JP) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
1425 K STREET, N.W.
SUITE 800
WASHINGTON
DC
20005
US
|
Assignee: |
POWDERTECH CO., LTD.
Chiba
JP
|
Family ID: |
35705248 |
Appl. No.: |
11/272024 |
Filed: |
November 14, 2005 |
Current U.S.
Class: |
430/111.32 ;
430/137.13 |
Current CPC
Class: |
G03G 9/1139 20130101;
G03G 9/1135 20130101; G03G 9/1134 20130101; G03G 9/1075
20130101 |
Class at
Publication: |
430/111.32 ;
430/137.13 |
International
Class: |
G03G 9/113 20060101
G03G009/113 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2004 |
JP |
JP2004-327385 |
Claims
1. A resin-coated ferrite carrier for an electrophotographic
developer, wherein the surface of each ferrite particle is coated
with a mixed resin of a tetrafluoroethylene-hexafluoropropylene
copolymer or a tetrafluoroethylene-perfluoroalkylvinyl ether
copolymer and a polyamideimide resin, the mixed resin containing a
silicon oxide.
2. The resin-coated ferrite carrier for an electrophotographic
developer according to claim 1, wherein the mixing weight ratio of
the tetrafluoroethylene-hexafluoropropylene copolymer or the
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer to the
polyamideimide resin in the mixed resin is 9:1 to 6:4.
3. The resin-coated ferrite carrier for an electrophotographic
developer according to claim 1, wherein the silicon oxide is
contained in an amount of 0.1 to 5 wt. % in the mixed resin.
4. The resin-coated ferrite carrier for an electrophotographic
developer according to claims 1, wherein the mixed resin is coated
in an amount of 0.01 to 10 wt.% based on the ferrite particle.
5. A method for producing a resin-coated ferrite carrier for an
electrophotographic developer, comprising: preparing a resin
solution containing a polyamideimide resin dissolved in an aqueous
solvent; dispersing a tetrafluoroethylene-hexafluoropropylene
copolymer or a tetrafluoroethylene-perfluoroalkylvinyl ether
copolymer and a silicon oxide in the resin solution to prepare a
resin-containing aqueous solution; and coating the resins on the
surface of each ferrite particle by using the aqueous solution.
6. An electrophotographic developer comprising the resin-coated
ferrite carrier according to claim 1 and a toner.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a resin-coated ferrite
carrier for a two-component electrophotographic developer used for
copying machines, printers and the like, its production method, and
an electrophotographic developer using the ferrite carrier, and
relates in detail to a resin-coated ferrite carrier which is
uniform and does not have problems of offensive odors and the like,
its production method, and an electrophotographic developer which
uses the ferrite carrier, has favorable characteristics in a long
period, and can fully respond to the high-speed and full-color.
[0003] 2. Description of the Related Art
[0004] The two-component developer used in electrophotography is
constituted of a toner and a carrier; the carrier is mixed and
agitated with the toner in a developer box; the toner is given a
desired charge; and the charged toner is carried to an
electrostatic latent image on a photoreceptor whereby the developer
is a carrier material to form a toner image. The carrier is, after
having formed the toner image, held by a magnet and stays on a
development roll, further returned to the developer box, again
mixed and agitated with new toner particles, and repeatedly used in
a certain period.
[0005] The two-component developer, different from a one-component
developer, is one in which the carrier agitates the toner
particles, imparts a desired chargeability, and has a function of
transporting the toner, has good controllability in developer
design, and is therefore widely used in the fields of full-color
machines requiring high-quality images and high-speed machines
requiring reliability and durability of image sustainability.
[0006] In such a two-component electrophotographic developer, an
iron-based carrier such as an oxide-coated iron powder and a
resin-coated iron powder has been used. Patent Document 1 (Japanese
Patent Laid-Open No. 6-19214) describes a carrier for full-color
copying machines in which a mixture of an iron powder and a
spherical ferrite particles is used as the carrier core material,
and the coating resin is composed of two layers with the under
coating material of a tetrafluoroethylenic resin containing a
polyamideimide resin and the surface coating material of a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin.
[0007] Since the iron-based carrier as described in Patent Document
1 has a large true specific gravity of one particle and then
imparts a large stress on a developing machine, the life-elongation
is difficult. Further, the resin-coated carrier composed of two
layers raises a problem of layer exfoliation.
[0008] Then, ferrite carriers such as Cu--Zn ferrite and Ni--Zn
ferrite, which have a lower true specific gravity than the
iron-based carrier, are used. These ferrite carriers also have many
characteristics advantageous over the conventional iron
powder-based carrier in obtaining high-quality images.
[0009] As these ferrite carriers, spherical ones are commonly used.
However, since the spherical ferrites alone are inferior in the
resistance against toner spent, they cannot respond to resent
year's higher durability.
[0010] Therefore, resin-coated ferrite carriers are used which have
the carrier core material of ferrite particles surface-coated with
a resin. As the coating resin used here, a silicone resin, a
fluorinated epoxy resin and the like are used.
[0011] However, resin-coated ferrite carriers coated with a
silicone resin have raised problems of fogging in copy images and
carrier adhesion due to the change in charge quantity which is
caused by internal temperature rise in continuous printing. On the
other hand, the resin-coated carriers coated with a fluorinated
epoxy resin have raised problems of toner scattering and fogging in
copy images due to a decreased charge of the toner spent by
continuous printing, and have also shown a faster loss of charge
over time, thus inferior in durability. Further, in the case of
using the fluorinated epoxy resin, the solvent needs to include an
organic solvent with a strong odor such as methyl isobutyl ketone,
and this case has problems of offensive odors and the like on
production.
[0012] Hence, use of a fluororesin as the coating resin is
proposed. Patent Document 2 (Japanese Patent Laid-Open No.
55-67754) describes a developer using a carrier whose core is
covered with a resinous coating composed of a
polytetrafluoroethylene of 5 to 55%, a fluorinated
polyethylenepropylene of 5 to 55% and a poly(amide-imide).
[0013] However, the carrier core material used in Patent Document 2
is carrier beads, not ferrite particles. Besides, the coating resin
used in Patent Document 2 includes a polytetrafluoroethylene, and
when the coating resin including a polytetrafluoroethylene is
coated on a carrier core material, the coating resin becomes
clayey, and does not provide a good coating. Thus, developers using
such resin-coated carriers are inferior in various properties.
[0014] Patent Document 3 (Japanese Patent Laid-Open No. 54-126040)
describes a carrier material for an electrophotographic developer
in which a skin layer composed of a material including a
fluoropolymer is provided on the surface of a carrier core material
via an intermediate layer including a resin which has a lower
melting point and a larger dielectric constant than the
fluoropolymer. Then, a polyamide resin and an ethylene-vinylacetate
resin are exemplified as the intermediate layer.
[0015] However, the carrier core material used in Patent Document 3
is steel beads, not ferrite particles (referring to the example) .
Further, the resin-coated carrier composed of two layers raises a
problem of the interlayer exfoliation, and does not use a
polyamideimide resin as a component of the coating resin.
[0016] Although various attempts using a resin-coated carrier have
been performed in such manners, a resin-coated carrier has not been
obtained which provides uniform coating, raises no problem of
offensive odor, and exhibits various favorable properties in a long
period when made into an electrophotographic developer.
[0017] On the other hand, Patent Document 4 (Japanese Patent
Laid-Open No. 2002-148869) describes a coating resin layer of a
resin-coated carrier which includes a fluororesin, a binder resin
and silica particles having a particular specific surface area and
a particular average particle size. It states that the silica
particles prevent the spent by the toner against the carrier
surface through the synergistic action with the fluororesin, and
impart a favorable fluidity of the carrier.
[0018] However, even in this Patent Document 4, a resin-coated
carrier, as in the case described above, has not been obtained
which provides uniform coating, raises no problem of offensive
odors, and exhibits various favorable properties in a long period
when made into an electrophotographic developer.
[0019] Therefore, the present invention has on object to provide a
resin-coated ferrite carrier having a uniform resin coating and
emitting no offensive odors and the like, its production method,
and an electrophotographic developer comprises the resin-coated
ferrite carrier, is excellent in the charge stability and the image
quality stability in a long period, causes less fogging of image or
carrier adhesion, has a favorable image density and environmental
dependability, and can fully respond to high-speed and full-color
imaging.
SUMMARY OF THE INVENTION
[0020] As the result of the extensive studies by the present
inventors, we have found that the above object can be achieved by
coating the surface of ferrite particles (carrier core material)
with a resin-containing aqueous solution obtained by dispersing a
specific fluororesin and a silicon oxide in a resin solution in
which a binder resin is dissolved in a water-based solvent, and
thus achieved the present invention.
[0021] That is, the present invention provides a resin-coated
ferrite carrier for an electrophotographic developer characterized
in that the surfaces of ferrite particles are coated with a mixed
resin of a tetrafluoroethylene-hexafluoropropylene copolymer or a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer with a
polyamideimide resin, and the mixed resin contains a silicon
oxide.
[0022] In the resin-coated ferrite carrier according to the present
invention, the mixing weight ratio of the
tetrafluoroethylene-hexafluoropropylene copolymer or the
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer to a
polyamideimide resin in the mixed resin is preferably 9:1 to
6:4.
[0023] In the resin-coated ferrite carrier according to the present
invention, the above silicon oxide is preferably contained in an
amount of 0.1 to 5 wt. % in the mixed resin.
[0024] In the resin-coated ferrite carrier according to the present
invention, the above mixed resin is coated preferably in an amount
of 0.01 to 10 wt. % based on the ferrite particles.
[0025] The present invention also provides a production method of a
resin-coated ferrite carrier for an electrophotographic developer
characterized in that a resin-containing aqueous solution prepared
by dissolving a tetrafluoroethylene-hexafluoropropylene copolymer
or a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer and a
silicon oxide in a resin solution containing a polyamideimide resin
dissolved in an aqueous solvent, and the surface of ferrite
particles is coated with the above resin by using the aqueous
solution.
[0026] The present invention also provides an electrophotographic
developer composed of the above resin-coated ferrite carrier and a
toner.
[0027] A method for producing a resin-coated ferrite carrier
according to the present invention provides a uniform resin coating
on the surface of carrier particles, and raises no problems of
offensive odors and the like caused by an organic solvent because a
water-based solvent is used. An electrophotographic developer using
a resin-coated ferrite carrier according to the present invention
is excellent in the charge stability and the image quality
stability in a long period, has little fog and carrier adhesion,
and has a favorable image density and environmental
dependability.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Hereinafter, the best embodiments to practice the present
invention will be illustrated.
<A Resin-Coated Ferrite Carrier According to the Present
Invention>
[0029] A resin-coated ferrite carrier according to the present
invention is one in which the surface of ferrite particles (carrier
core material) is coated with a mixed resin of a
tetrafluoroethylene-hexafluoropropylene copolymer or a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer with a
polyamideimide resin.
[0030] The composition of the ferrite particles (carrier core
material) used in the present invention is not especially limited,
but preferably one expressed by the following formula (1).
(MnO).times.(MgO)y(Fe.sub.2O.sub.3)z (1)
[0031] (wherein, x+y+z=100 mol %; x=35 to 45 mol %; y=5 to 15 mol
%; and z=40 to 55 mol %)
[0032] For (MnO) and/or a part of (MgO) in the above formula (1),
at least one of oxides selected from SrO, Li.sub.2O, CaO, TiO, CuO,
ZnO, NiO, Bi.sub.2O.sub.3 and ZrO.sub.2 may be substituted.
[0033] Since the ferrite particles of such specific composition
have a high magnetization and the excellent homogeneity of
magnetization (little variations in magnetization), they are
favorably used in the present invention.
[0034] A tetrafluoroethylene-hexafluoropropylene copolymer
(hereinafter, may be referring to as FEP) used in the present
invention is a fluorine-based resin having a melting point of 250
to 270.degree. C. A tetrafluoroethylene-perfluoroalkylvinyl ether
copolymer (hereinafter, maybe referring to as PFA) used in the
present invention is a fluorine-based resin having a melting point
of 300 to 310.degree. C.
[0035] A polyamideimide resin used in the present invention is used
as the binder resin, and is not especially limited in the
production method, properties, etc., but is typically a copolymer
of trimellitic anhydride and an organic bisamine, for example,
4,4'-diaminodiphenylmethane. The average molecular weight of such a
copolymer is typically 15,000 to 30,000, preferably 20,000 to
25,000. Alternatively, a copolymer of pyromellitic anhydride and a
bisamine, especially an aromatic bisamine can be used. Use of such
polyamideimide resin as the binder resin imparts a high
chargeability, a stability against in-machine environmental changes
and a favorable spent resistance.
[0036] The mixing weight ratio of the
tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or the
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA) to
the polyamideimide resin in the above mixed resin is preferably 9:1
to 6:4, more preferably 8:2 to 6:4. When the mixing amount of FEP
or PFA is less than the above range in the mixing weight ratio of
FEP or PFA and the polyamideimide resin, the spent resistance and
the charge stability deteriorate, and when the mixing amount
exceeds the above range, the durability decreases.
[0037] In a resin-coated ferrite carrier according to the present
invention, a silicon oxide is contained in the mixed resin. With a
silicon oxide contained in a mixed resin, a uniform resin coating
can be obtained, and the adhesiveness with core particles is
improved. The content of the silicon oxide is preferably 0.1 to 5
wt. % in the mixed resin. With the silicon oxide content of less
than 0.1 wt. %, the effect of the content disappears, and with that
exceeding 5 wt. %, the durability decreases.
[0038] The mixed resin is coated preferably in an amount of 0.01 to
10 wt. % based on the ferrite particles (carrier core material),
further preferably 0.3 to 7 wt. %, and most preferably 0.5 to 5 wt.
%. With the coating amount of less than 0.01 wt. %, the formation
of a uniform coating layer on the carrier surface becomes
difficult. With that exceeding 10 wt. %, the cohesion of the
carriers are generated, thereby decreasing the productivity such as
the yield and also causing the variations in the developer
properties such as fluidity and charge quantity in actual
machines.
[0039] A resin-coated ferrite carrier according to the present
invention is desirably spherical, and the average particle size is
preferably 20 to 100 .mu.m, more preferably 30 to 70 .mu.m. With
the average particle size of less than 20 .mu.m, the carrier
adhesion is apt to occur, and white spots are caused. With that
exceeding 100 .mu.m, the image quality becomes coarse, and the
desired definition becomes hard to obtain.
[0040] Further, in the above coating resin, a silane coupling agent
can be contained as a charge controlling agent. The kind of a
usable coupling agent is not especially limited, but is preferably
an aminosilane coupling agent in the case of negative polarity
toner, and a fluorine-based silane coupling agent in the case of
positive polarity toner.
[0041] Further, in the above coating resin, conductive
microparticles can be charged. The microparticles include
conductive carbon, an oxide such as titanium oxide and tin oxide,
and various kinds of organic conductive agents.
<A Method for Producing a Ferrite Carrier for a Developer
According to the Present Invention >
[0042] Next, a method for producing a resin-coated ferrite carrier
according to the present invention will be illustrated.
[0043] First, a ferrite raw material is weighed appropriately to a
predetermined composition, and then pulverized and mixed by a ball
mill, a vibrating mill or the like for at least 0.5 h, preferably
for 1 to 20 h. The pulverized material thus obtained is pelletized
by a press or the like, and thereafter calcined at a temperature of
700 to 1,200.degree. C. Instead of using a press, after
pulverization, the product may be charged with water to make a
slurry, and granulated by using a spray drier. When the apparent
density is desired to be kept low, the calcination step can be
omitted.
[0044] After the calcination, it is further pulverized by a ball
mill, a vibrating mill or the like, and there after the resulting
pulverized material is charged with water, and optionally a
dispersant, a binder and the like, granulated after the viscosity
adjustment, and kept at a temperature of 1,000 to 1,500.degree. C.
for 1 to 24 h with the oxygen concentration controlled and
sintered. When pulverized after the calcination, it may be charged
with water and pulverized by a wet ball mill, a wet vibrating mill
or the like.
[0045] The sinter obtained in such a manner is pulverized and
classified. The classifying method involves adjusting the particle
size to a desired one by using the existing air classification,
mesh filtration, precipitation method or the like.
[0046] Thereafter, the classified particles may optionally undergo
oxide coating by heating their surfaces to a low temperature to
adjust electric resistance. The oxide coating requires a common
type of electric furnace such as a rotary electric furnace and a
batch-type electric furnace, and the heat treatment is conducted at
a temperature of 300 to 700.degree. C., for example. The thickness
of the oxide coating formed by this treatment is preferably 0.1 nm
to 5 .mu.m. If the thickness is less than 0.1 nm, the effect of the
oxide coating layer is little. If that exceeds 5 .mu.m, since the
magnetization decreases, and the resistance becomes too high,
disadvantages such as the decrease in developing capacity are apt
to take place. The reduction may be optionally conducted prior to
oxide coating.
[0047] Next, on the surface of the above ferrite particles (carrier
core material), a mixed resin (coating resin) containing a
polyamideimide resin is coated. In the production method according
to the present invention, a resin-containing aqueous solution is
prepared by dispersing the FEP or PFA and silicon oxide, described
above, in a resin solution in which the polyamideimide resin is
dissolved in a water-based solvent, and the above mixed resin is
coated on the surface of the above ferrite particles by using the
aqueous solution. When a fluorinated epoxy resin is used as a resin
to coat the surface of the ferrite particles, it is necessary for
the solvent to contain an organic solvent strong in odor intensity
such as methyl isobutyl ketone, which has raised problems of
offensive odors, etc. in their production. By contrast, since a
water-based solvent can be used because the mixed resin used in the
present invention is soluble in water, the problems above do not
arise. When an electrophotographic developer is manufactured,
various properties are also improved.
[0048] Known coating methods may be used, for example, brush
coating, fluidized bed spray drying, rotary drying, and
immersion/drying using a universal stirrer. The fluidized bed
process is more preferable due to a higher coverage of coating.
[0049] In the case where the resin is cured after coated on the
carrier core material, an externally heating system and an
internally heating system both can be used for curing. For example,
a fixed-type or flow-type electric furnace, a rotary electric
furnace, a burner furnace or the microwave can be used for
curing.
<An Electrophotographic Developer According to the Present
Invention>
[0050] An electrophotographic developer according to the present
invention will be illustrated.
[0051] An electrophotographic developer according to the present
invention is composed of the resin-coated ferrite carrier described
above and a toner.
[0052] Toner particles constituting a developer according to the
present invention come in pulverized toner particles manufactured
by the pulverizing method and polymerized toner particles
manufactured by the polymerization method. The toner particles by
both methods can be used in the present invention.
[0053] Pulverized toner particles can be obtained by fully mixing,
for example, a binding resin, a charge controlling agent, and a
colorant by a Henschel mixer or the like, then melting and kneading
by a biaxial extruder or the like, and after cooling, pulverizing,
classifying, and after adding an additive, mixing by a mixer or the
like.
[0054] The binding resin constituting pulverized toner particles is
not especially limited, but includes a polystyrene,
chloropolystyrene, styrene-chlorostyrene copolymer,
styrene-acrylate copolymer, styrene-methacrylate copolymer, further
a rosin-modified maleic acid resin, epoxy resin, polyester resin
and polyurethane resin. These are used alone or by mixing.
[0055] Any charge controlling agent can be used. The agent for a
positively chargeable toner includes, for example, a nigrosine dye,
a quaternary ammonium salt, etc. The one for a negatively
chargeable toner includes a metal-containing monoazo dye, etc.
[0056] As the colorant (coloring agent), conventionally known dyes
and pigments are usable. For example, carbon black, phthalocyanine
blue, permanent red, chrome yellow, phthalocyanine green, etc. can
be used. Additionally, an additive such as silica powder and
titania to improve the fluidity and cohesion resistance of a toner
can be charged corresponding to the toner particles.
[0057] The polymerized toner particles come in toner particles
manufactured by conventional methods such as the suspension
polymerization method, emulsion polymerization method, emulsion
coagulation method, ester elongation polymerization method and
emulsion phase inversion method. Such toner particles by the
polymerization method are obtained, for example, by mixing and
agitating a colored dispersion liquid in which a colorant is
dispersed in water using a surfactant, a polymerizable monomer, a
surfactant and a polymerization initiator in an aqueous medium,
emulsifying and dispersing the polymerizable monomer in the aqueous
medium, polymerizing while agitating and mixing, adding a salting
agent and salting out the polymerized particles, and filtrating,
washing and drying the particles obtained by the salting-out.
Thereafter, the dried toner particles are optionally charged with
an additive.
[0058] Further, on production the polymerized toner particles, a
fixation improving agent and a charge controlling agent can be
blended other than the polymerizable monomer, surfactant,
polymerization initiator and colorant, thus allowing to control and
improve various properties of the polymerized toner particles
obtained using these. Besides, for improving the dispersibility of
the polymerizable monomer in the aqueous medium, and adjusting the
molecular weight of the obtained polymer, a chain-transfer agent
can be used.
[0059] The polymerizable monomer used for the manufacture of the
above polymerized toner particles is not especially limited, but
includes, for example, styrene and its derivative, ethylenic
unsaturated monoolefins such as ethylene, propylene, halogenated
vinyls such as vinyl chloride, vinylesters such as vinyl acetate,
and a-methylene aliphatic monocarboxylate such as methyl acrylate,
ethyl acrylate, methyl methacrylate, ethyl methacrylate,
2-ethylhexyl methacrylate, acrylic acid dimethylamino ester and
methacrylic acid diethylamino ester.
[0060] As the colorant (coloring material) used for preparing the
above polymerized toner particles, conventionally known dyes and
pigments are usable. For example, carbon black, phthalocyanine
blue, permanent red, chrome yellow and phthalocyanine green can be
used. These colorants may be improved in the surface thereof by
using a silane coupling agent, a titanium coupling agent and the
like.
[0061] As the surfactant used for production the above polymerized
toner particles, ananionicsurfactant, acationic surfactant, an
amphoteric surfactant and a nonionic surfactant can be used.
[0062] Here, the anionic surfactants include sodium oleate, a fatty
acid salt such as castor oil, an alkylsulfate such as sodium
laurylsulfate and ammonium laurylsulfate, alkylbenzene sulfonate
salts such as sodium dodecylbenzene sulfonate, an alkylnaphthalene
sulfonate salt, an alkylphosphate salt, a naphthalene sulfonic
acid-formalin condensate, a polyoxyethylene alkylsulfate salt, etc.
The nonionic surfactants include a polyoxyethylene alkyl ether, a
polyoxyethylene aliphatic acid ester, a sorbitan aliphatic acid
ester, a polyoxyethylene alkyl amine, glycerin, an aliphatic acid
ester, an oxyethylene-oxypropylene block polymer, etc. Further, the
cationic surfactants include alkylamine salts such as laurylamine
acetate, and quaternary ammonium salts such as
lauryltrimethylammonium chloride, stearyltrimethylammonium
chloride, etc. Then, the amphoteric surfactants include an
aminocarbonate salt, an alkylamino acid, etc.
[0063] A surfactant as above is generally used in an amount within
the range of 0.01 to 10 wt. % to apolymerizable monomer. Since the
use amount of such a surfactant affects the dispersion stability of
a monomer, and affects the environmental dependability of the
obtained polymerized toner particles, it is preferably used in the
amount within the above range where the dispersion stability of the
monomer is secured, and the polymerized toner particles do not
excessively affect the environmental dependability.
[0064] For production polymerized toner particles, a polymerization
initiator is generally used. The polymerization initiators come in
a water-soluble polymerization initiator and an oil-soluble
polymerization initiator, and both of them can be used in the
present invention. The water-soluble polymerization initiator used
in the present invention includes, for example, a peroxosulfate
salt such as potassium peroxosulfate, and ammonium peroxosulfate,
and a water-soluble peroxide compound. The oil-soluble
polymerization initiator includes, for example, an azo compound
such as azobisisobutyronitrile, and an oil-soluble peroxide
compound.
[0065] In the case where a chain-transfer agent is used in the
present invention, the chain-transfer agent includes, for example,
mercaptans such as octylmercaptan, dodecylmercaptan, and
tert-dodecylmercaptan, carbon tetrabromide, etc.
[0066] Further, in the case where polymerized toner particles used
in the present invention contain a fixation improving agent, as the
fixation improving agent, a natural wax such as a carnauba wax, and
an olefinic wax such as a polypropylene and a polyethylene can be
used.
[0067] In the case where polymerized toner particles used in the
present invention contain a charge controlling agent, the charge
controlling agent to be used is not especially limited, and a
nigrosine dye, quaternary an ammonium salt, an organic metal
complex, a metal-containing monoazo dye and the like can be
used.
[0068] The additive used for improving the fluidity etc. of
polymerized toner particles includes silica, titanium oxide, barium
titanate, fluororein microparticles, acrylic acid resin
microparticles, etc., and these can be used alone or in combination
thereof.
[0069] Further, the salting-out agent used for separating
polymerized particles from an aqueous medium includes metal salts
such as magnesium sulfate, aluminum sulfate, barium chloride,
magnesium chloride, calcium chloride and sodium chloride.
[0070] The average particle size of the toner particles
manufactured as above is in the range of 2 to 15 .mu.m, preferably
in the range of 3 to 10 .mu.m. The polymerized toner particles have
the higher uniformity than the pulverized toner particles. The
toner particles of less than 2 .mu.m decrease the charging capacity
and are apt to bring about fog and toner scattering. Those
exceeding 15 .mu.m cause the degradation of image quality.
[0071] By mixing the carrier and the toner manufactured as above,
an electrophotographic developer is obtained. The mixing ratio of
the carrier to the toner, namely, the toner concentration, is
preferably set to be 3 to 15%. With less than 3%, a desired image
density is hard to obtain. With more than 15%, the toner scattering
and fog are apt to occur.
[0072] The developer prepared as above can be used in copying
machines, printers, FAXs, printing presses and the like, in the
digital system, which use the development system in which
electrostatic latent images formed on a latent image holder having
an organic photoconductor layer are reversal developed by magnetic
brushes of the two-component developer having the toner and the
carrier while impressing a bias electric field. It is also
applicable to full-color machines and the like which use an
alternating electric field, which is a method to superimpose an AC
bias on a DC bias, when the developing bias is applied from
magnetic brushes to electrostatic latent image side.
[0073] Hereinafter, the present invention will be specifically
illustrated by way of examples.
EXAMPLE 1
CARRIER PRODUCTION EXAMPLES 1
[0074] Raw materials of 39.7 mol % in terms of MnO, 9.9 mol % in
terms of MgO, 49.6 mol % in terms of Fe.sub.2O.sub.3 and 0.8 mol %
in terms of SrO were blended in proper amount, charged with water,
and pulverized, mixed and dried in a wet ball mill for 10 h, kept
at 950.degree. C. for 4 h, and then pulverized in a wet ball mill
for 24 h to obtain a slurry. Then the slurry were granulated and
spray-dried, kept at 1,270.degree. C. for 6 h in an atmosphere of
an oxygen concentration of 2%, and then crushed and adjusted for
particle size to obtain manganese-based ferrite particles (carrier
core material). The manganese ferrite particles had an average
particle size of 35 .mu.m and a saturation magnetization of 70
Am.sup.2/kg at an applied magnetic field of 3,000
(10.sup.3/4.pi.A/m).
[0075] Then, a polyamidoimido resin (a copolymer of trimellitic
acid anhydride and 4,4'-diaminodiphenylmethane) was diluted with
water to prepare a resin solution, in which a
tetrafluoroethylene-hexafluoropropylene copolymer (FEP) was then
dispersed, and a silicon oxide (2 wt. % of the total resin amount)
was further dispersed to obtain a coating layer forming solution of
150 g in terms of solid content. The solid content ratio of the
resin solution was 10 wt. %. The weight composition ratio of the
polyamideimide resin to the FEP was 2/8. The coating layer forming
solution and 10 kg of the ferrite particles described above were
together charged in a fluidized-bed coater to perform coating.
Thereafter, it was cured at 250.degree. C. for 1 h to manufacture a
resin-coated ferrite carrier 1 having a coated resin amount of 1.5
wt. %.
DEVELOPER PRODUCTION EXAMPLES 1
[0076] A developer "A" having a toner concentration of 6 wt. % was
prepared using the above carrier 1 and a toner 1 (KM-C2630 toner,
manufactured by Kyocera Mita Corp., color: magenta, composition:
polyester, production method: pulverizing method). The image
evaluation at an early stage and after 100,000 times was conducted
by a KM-C2630 (manufactured by Kyocera Mita Corp.) as an evaluation
instrument. The image evaluation at an early stage was conducted
for the charge quantity, toner concentration, image density, fog,
image quality and carrier adhesion; the image evaluation after
100,000 times was conducted for the charge quantity, toner
concentration, image density, fog, image quality, environmental
dependency and carrier adhesion. The results are shown in Table 1.
The evaluation methods were as follows.
[0077] (Charge Quantity)
[0078] The charge quantities were measured by a Q/M meter,
manufactured by Epping GmbH.
[0079] (Image Density)
[0080] The developments were conducted under an optimum exposure
condition. The image densities of the solid part were measured by
an X-Rite938, manufactured by Nippon Lithograph Inc., and ranked.
The target value of the image density is at least 1.25.
[0081] (Fog)
[0082] The fogs were measured by a color-difference meter Z-300A,
manufactured by Nippon Denshoku Kogyo KK. The target value of the
fog is at most 5.
[0083] (Image Quality)
[0084] The developments were conducted under an optimum exposure,
and the image qualities were visually judged, and evaluated on the
following standard.
[0085] G: good
[0086] M: no problem in the practical use
[0087] P: not usable
[0088] (Carrier Adhesion)
[0089] The developments were conducted under an optimum exposure
condition, and the levels of carrier adhesion on images and white
spots were visually judged, and evaluated on the following
standard.
[0090] G: good
[0091] M: no problem in the practical use
[0092] P: not usable
[0093] (Environmental Dependability)
[0094] The developments were conducted under L/L and H/H
environments and under an optimum exposure, and the image qualities
were visually judged, and evaluated on the following standard.
[0095] G: good
[0096] M: no problem in the practical use
[0097] P: not usable
EXAMPLE 2
CARRIER PRODUCTION EXAMPLE 2
[0098] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 2 having a
coated resin amount of 1.5 wt. % as in Example 1, but using a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA)
instead of FEP as the fluororesin.
DEVELOPER PRODUCTION EXAMPLE 2
[0099] A developer B having a toner concentration of 6 wt. % was
prepared using the above carrier 2 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
EXAMPLE 3
CARRIER PRODUCTION EXAMPLE 3
[0100] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 3 having a
coated resin amount of 1.5 wt. % as in Example 1, but with the
mixing weight ratio of the polyamideimide resin to the
tetrafluoroethylene-hexafluoropropylene copolymer (FEP) being
changed to 4/6.
DEVELOPER PRODUCTION EXAMPLE 3
[0101] A developer C having a toner concentration of 6 wt. % was
prepared using the above carrier 3 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
EXAMPLE 4
CARRIER PRODUCTION EXAMPLE 4
[0102] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 4 having a
coated resin amount of 1.5 wt. % as in Example 1, but using
methylethylketone instead of water as the solvent.
DEVELOPER PRODUCTION EXAMPLE 4
[0103] A developer D having a toner concentration of 6 wt. % was
prepared using the above carrier 4 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
EXAMPLE 5
CARRIER PRODUCTION EXAMPLE 5
[0104] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 5 having a
coated resin amount of 1.5 wt. % as in Example 1, but with the
mixing weight ratio of the polyamideimide resin to the
tetrafluoroethylene-hexafluoropropylene copolymer (FEP) being
changed to 6/4.
DEVELOPER PRODUCTION EXAMPLE 5
[0105] A developer E having a toner concentration of 6 wt. % was
prepared using the above carrier 5 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
EXAMPLE 6
CARRIER PRODUCTION EXAMPLE 6
[0106] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 6 having a
coated resin amount of 1.5 wt. % as in Example 1, but with the
silicon oxide content being changed to 6 wt. % of the total
resin.
DEVELOPER PRODUCTION EXAMPLE 6
[0107] A developer F having a toner concentration of 6 wt. % was
prepared using the above carrier 6 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
COMPARATIVE EXAMPLE
COMPARATIVE EXAMPLE 1
CARRIER PRODUCTION COMPARATIVE EXAMPLE 7
[0108] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 7 having a
coated resin amount of 1.5 wt. % as in Example 1, but using
tetrafluoroethylene resin (PTFE) instead of FEP as the
fluororesin.
DEVELOPER PRODUCTION COMPARATIVE EXAMPLE 7
[0109] A developer G having a toner concentration of 6 wt. % was
prepared using the above carrier 7 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
COMPARATIVE EXAMPLE 2
CARRIER PRODUCTION COMPARATIVE EXAMPLE 8
[0110] Ferrite particles were manufactured by the method as in
Example 1. A mixed resin was coated on the surface of the carrier
particles to manufacture a resin-coated ferrite carrier 8 having a
coated resin amount of 1.5 wt. % as in Example 1, but using an
epoxy resin instead of the polyamideimide resin as the binder
resin.
DEVELOPER PRODUCTION COMPARATIVE EXAMPLE 8
[0111] A developer H having a toner concentration of 6 wt. % was
prepared using the above carrier 8 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
COMPARATIVE EXAMPLE 3
CARRIER PRODUCTION COMPARATIVE EXAMPLE 9
[0112] A carrier core material was manufactured by mixing the
ferrite particles manufactured by the method as in Example 1 with a
flat iron powder (mixing weight ratio 40/60).
[0113] Then, the mixed resin was coated on the surface of the
carrier core material to manufacture a resin-coated ferrite carrier
9 having a coated resin amount of 1.5 wt. % as in Example 1.
DEVELOPER PRODUCTION COMPARATIVE EXAMPLE 9
[0114] A developer I having a toner concentration of 6 wt. % was
prepared using the above carrier 9 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1.
COMPARATIVE EXAMPLE 4
CARRIER PRODUCTION COMPARATIVE EXAMPLE 10
[0115] A carrier core material was manufactured by mixing the
ferrite particles manufactured by the method as in Example 1 with a
spherical magnetite (mixing weight ratio 20/80).
[0116] Then, the mixed resin was coated on the surface of the
carrier core material to manufacture a resin-coated ferrite carrier
10 having a coated resin amount of 1.5 wt. % as in Example 1.
DEVELOPER PRODUCTION COMPARATIVE EXAMPLE 10
[0117] A developer J having a toner concentration of 6 wt. % was
prepared using the above carrier 10 and the same toner 1 as used in
Example 1. The image evaluations at an early stage and after
100,000 times were conducted as in Example 1. The results are shown
in Table 1. TABLE-US-00001 TABLE 1 After 100,000 times Envi- At an
early stage ron- Car- Charge Toner Image Image Carrier Charge Toner
Image Image mental rier Devel- quan- concen- den- qual- adhe- quan-
concen- den- qual- depend- adhe- oper Carrier tity tration sity Fog
ity sion tity tration sity Fog ity ability sion Example 1 A Carrier
22.5 5.8 1.49 0 G G 20.8 5.6 1.47 1 G G G 1 Example 2 B Carrier
20.3 5.7 1.43 0 G G 18.7 5.4 1.45 1 G G G 2 Example 3 C Carrier
18.4 5.7 1.45 0 G G 17.5 5.40 1.43 1 G G G 3 Example 4 D Carrier
17.8 5.6 1.45 1 G G 16.3 5.50 1.45 2 G M G 4 Example 5 E Carrier
16.7 5.6 1.52 1 G G 12.0 5.7 1.59 5 M M G 5 Example 6 F Carrier
18.6 5.7 1.44 0 G G 12.5 6.20 1.59 5 M M M 6 Compara- G Carrier
20.3 5.7 1.48 2 G G 9.2 6.5 1.62 5 M M M tive 7 Example 1 Compara-
H Carrier 12.2 5.7 1.55 2 M G 6.7 6.4 1.64 8 M P P tive 8 Example 2
Compara- I Carrier 15.8 5.5 1.56 2 M G 8.5 4.9 1.6 7 P P G tive 9
Example 3 Compara- J Carrier 19.0 5.7 1.5 2 M G 10.1 5 1.6 6 P P G
tive 10 Example 4
[0118] As clarified from the results in Table 1, Examples 1 to 6
maintain high charge quantities with elapsed times, and are
favorable in the fog, image quality, environmental dependability
and carrier adhesion. In particular, Examples 1 to 3, where the
production method according to the present invention is used, and
the mixing weight ratio of the polyamideimide resin to the
tetrafluoroethylene-hexafluoropropylene copolymer (FEP) is in a
certain range, and the content of the silicon oxide is in a
specific range, exhibit excellent properties. By contrast,
Comparative Examples 1 to 4 exhibit the decrease in charge
quantities with elapsed times, and are inferior in the fog, image
quality, environmental dependency, etc.
[0119] The production method of the resin-coated ferrite carrier
according to the present invention provides a uniform resin coating
on the surface of carrier particles, and raises no problems such as
offensive odors, etc. caused by an organic solvent because a
water-based solvent is used. The electrophotographic developer
using the resin-coated ferrite carrier according to the present
invention is excellent in the charge stability and image quality
stability over a long period, further exhibits little fog and
carrier adhesion, and is favorable in the image density and
environmental dependency.
[0120] Therefore, the electrophotographic developer according to
the present invention is used for copying machines, printers and
the like, and can fully respond to the high-speed and full-color of
developing machines.
* * * * *